<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <ul>
        <li></li>
        <li></li>
        <li></li>
        <li></li>
        <li></li>
        <button></button>
    </ul>
    <ul></ul>

    <script>

        var liList = document.querySelectorAll('li') // 共5个li
        for (var i = 0; i < liList.length; i++) {
            liList[i].onclick = function () {
                console.log(i)
            }
        }
        var button = document.getElementsByTagName('button')
        for (let i = 0; i < 5; i++) {
            button[0].addEventListener('click', function () {
                console.log(i);

            })
        }


    </script>
</body>

</html>